Controlling Gene Expression Part A: In Prokaryotes
Controlling Gene ExpressionPart A: In Prokaryotes
Control Mechanismsin Prokaryotes
• not all proteins are needed by all cells at all times, so gene regulation is important to an organism's survival
Prokaryotic Cells• use operons to control gene expression • an operon is:
– one promoter region – an operator – a cluster of genes that follows
EXAMPLE 1 LAC Operon • lactose is a disaccharide found in milk or milk
sugars • bacteria cells metabolize lactose (into glucose and
galactose) to generate energy • The genes that regulate the metabolism of lactose
are only switched on when lactose is present.
lac operon• the lac operon contains:
– a promoter – an operator – 3 genes – a repressor protein
• lactose is the signal molecule, in this case it is an inducer
lac operon animation
trp operon animation
• Narrated animation: • https://highered.mheducation.com/olcweb/
cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120080/bio26.swf::The%20Tryptophan%20Repressor
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Create a VENN diagram comparing the lac and trp operon.
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Controlling Gene ExpressionPart B: in Eukaryotes
RNA polymerase
Transcription factors
Enhancers
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Transcription factors
» Start and stop the binding of RNA polymerase to start gene expression
» These factors are regulated by enhancers and enhancer regions which turn on and off transcription.
Transcriptional Regulation• dissociating DNA and histones to allow access to promoter
by transcription factors – Activator molecules/regulatory region remodeling
histones – addition of acetyl groups (exposes promoter sites)
• methylation -binds to C of DNA turns genes off
Agouti Mice are identical twins that have different rates of methylation and acetylation acquired through diet regulating the expression of their genes.
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Homework
» Read on ‘Impact of Environment of gene expression’, ‘ Patterns of methylation’ , and read sections on nucleosomes and the regulation of transcription
» DBQ on page 356 and page 358